Evidence for the existence of tumor-specific antigens (TSA) in animals is reviewed. The demonstration of similar antigens in man is hampered by both practical and ethical considerations. Tumor-associated substances have been found in man, generally by immunization of heterologous species. In relatively few instances such antigens have been detected by studying the immune response of patients to their tumors. This proposal is directed to the identification of tumor-related antigens in man which provoke humoral immunity. Once detected, the sequence for the characterization of antigens is outlined, including studies of their nature, specificity, and distribution. It is anticipated that most of the antigens found will be common to malignant tissues and not confined to a specific histologic category of neoplasm. Further characterization of the antigens already identified, S1, S2, and S3, is also proposed. The interests, experience, and history of productivity of this laboratory coincide with the needs of the Government.